New database trait (#5549)

* Introduce trait

* The trait

* Generic

* Basic impls.

* Remove unneeded bounds

* Minor changes

* Switch over to the new DB trait

* Integrated parity-db and added CLI for db selection

* Default impl.

* Fix logs.

* Started integrating subdb

* Apply suggestions from code review

Co-Authored-By: Cecile Tonglet <cecile@parity.io>

* Apply suggestions from code review

Co-Authored-By: Nikolay Volf <nikvolf@gmail.com>

* Enable subdb

* Bump parity-db

* Fixed CLI macro

* Fixed browser build

* Fixed features

* Sort out features

* Use parity-db from crates.io

* Typo

Co-authored-by: arkpar <arkady.paronyan@gmail.com>
Co-authored-by: Cecile Tonglet <cecile@parity.io>
Co-authored-by: Nikolay Volf <nikvolf@gmail.com>

substrate/client/cli/src/commands/purge_chain_cmd.rs

@@ -39,7 +39,7 @@ impl PurgeChainCmd {
 	/// Run the purge command
 	pub fn run(&self, config: Configuration) -> error::Result<()> {
 		let db_path = match &config.database {
-			DatabaseConfig::Path { path, .. } => path,
+			DatabaseConfig::RocksDb { path, .. } => path,
 			_ => {
 				eprintln!("Cannot purge custom database implementation");
 				return Ok(());